The invention relates to a component for an integrated optical system, in particular for guiding electromagnetic radiation in the visible and/or infrared wavelength range. The component comprises a monocrystalline substrate of a material having a garnet structure and a refractive index n.sub.1. The substrate is provided with a monocrystalline optical waveguide layer of refractive index n.sub.3.
Components for integrated optical systems require monocrystalline optical waveguide layers which may serve as (passive) optical waveguides or as active layers in electrooptical or magnetooptical devices. Optical waveguide experiments are described in Magnetic Bubble Technology: Integrated Circuit Magnetics for Digital Storage and Processing, edited by H. Chang (IEEE PRESS Selected Reprint Series, New York, 1975, pp. 111-116) in which light waves in the wavelength range between 1 and 5 .mu.m were propagated in Eu.sub.3 Ga.sub.5 O.sub.12 layers which had been grown epitaxially on Gd.sub.3 (Sc.sub.2 Al.sub.3)O.sub.12 substrates. Experiments are also described which relate to the switching and modulation of radiation of a He-Ne laser in a magnetooptically active waveguide which comprised a Y.sub.3 (Ga.sub.1.1 Sc.sub.0.4 Fe.sub.3.5)O.sub.12 layer (n=2.1) grown on a Gd.sub.3 Ga.sub.5 O.sub.12 substrate (n=1.94.+-.0.02).
In order to be able to conduct light, the waveguide layer must have a refractive index which is higher than that of the material surrounding the layer. This is achieved in the known (passive) optical waveguide in that an R.sub.3 Ga.sub.5 O.sub.12 layer (n=1.94.+-.0.02) is grown on an R.sub.3 (Sc.sub.2 Al.sub.3)O.sub.12 substrate (n=1.87.+-.0.02), where R represents a rare earth metal ion.
A first disadvantage of the known device is that R.sub.3 (Sc.sub.2 Al.sub.3)O.sub.12 has to be used as the substrate material. Gd.sub.3 Ga.sub.5 O.sub.12 cannot be used as a substrate because its refractive index (n=1.945) is too high with respect to the other waveguide layer R.sub.3 Ga.sub.5 O.sub.12 materials. Gd.sub.3 Ga.sub.5 O.sub.12 is presently the only garnet single crystal of a high-grade physical-optical optical quality which can be grown by the Czochralski method on a scale suitable for mass production.
A second disadvantage is that the difference between the refractive indices of the waveguide layer and of the substrate is comparatively small, so that the ability to contain light within the layer is not optimum.
With regard to the known magnetooptically active waveguide, the disadvantages mentioned above either do not exist or are less severe. However, the use of Y.sub.3 (Ga.sub.1.1 Sc.sub.0.4 Fe.sub.3.5)O.sub.12 as a material for the magneto-optically active layer has the disadvantage that the existing magnetic and magnetooptical properties, the optical absorption and the lattice constant of the material must be acceptable.